ELS detector gain

Hello.
When we use ELS detector in our UPLC system and raise the gain over 150 or so,
there's no signal obtained. It seems like it went out of the proper range somehow.
(No natural noises.)
Measurements can be done normally with lower gain.
What can be the reason and remedy?

Dear it’s the matter of sensitivity, when you increase the gain your sensitivity level increase & high gain in ELSD delivers maximum sensitivity with minimum baseline noise…. with or without injection, so lamp starts work according to that… your ELSD gain high so that baseline looks straight.

the gain is like you can say attenuation settings in UV..

i think 150 gain is very high...no signal will appear.... did you check Nitrogen? as ELSD requires high purity N2.. as you said, you getting noises at lower Gain... & temperature settings also important...?

We believe that what you are looking at is a large background that is being disguides by the autozero on injection. Whay we suspect is that by increasing the gain will only makes the PMT current (the ELS signal) larger. All PMT's will saturate if the gain is too large, which we suspect is the case here. The fact that the signals look "normal" at lower gains tends to suggest that the background is too big.

Note the ELSD does not discriminate between scattering of solvent droplets and scattering of analyte "slush balls." the drift tube temp should be high enough to desolvate but low enough to ensure that semi volatile peaks are preserved.

Thank you for your comment, Liz. We have tried as you have suggested.After disabling autozero, the ELS signal readings were high, close to2000 LSU.However, any change in ELS detector setting including drift tube and nebulizer temperature, as well as in solvent, did not lower the signalreadings. What should we do then?

Here's some chromatograms and conditions used, with our system,with the auto-zero turned off. Please see the file attached.Gain was set as 100, so the line barely goes within the range.But when we make the gain 150, it goes out of the range.

Some contamination in the drift tube or the nebulizer might besuspected, as some ghost (?) peaks appear even without injection. However, cleaning procedures that we are taught from Japanese Watersstaff did not make the situation better.

Thank you for the chromatograms and information and so now we have (of course) a few more questions to ask - apologies.

(1) Since the signal offset and the noise are so high, we are suspicious of the Normalization factor. Is it possible that you ran "Normalization" with liquid flow to the nebulizer? I do want to be confident that the instrument PMT was normalized properly, just to be sure can you run the normalization diagnostic once again. Ensure that the liquid flow off (no flow), with the gas flow set to something like 35 psi. The diagnostic itself has some instructions along the way.

(2) After this the next concern is that the nebulizer "off" cooling the nebulizer may reduce the background dramatically.

It took us a long time, as Waters (Japan) did not recommend us todo normalization of PMT by ourselves. A Waters staff visited usand normalized PMT, but the situation did not change. He recommendedus to send the detector back to Waters for checkup. So we did.Eventually, they told us that what have worked was the normalization of the lamp, not the PMT. Now our ELS detector works well.